Abstract: A smoke detection system comprises a manifold (4) connected to a series of sampling pipes (2). A fan (6) which draws a large volume of sampling air through the sampling pipes is connected to the inlet manifold and a small proportion of that air is directed to the inlet of a smoke detector (12), the outlet of which is connected to the manifold. The configuration obtained by the connection of the outlet from the detector into the inlet manifold provides a large pressure drop across the flow path through the detector. As a result of the large pressure drop, a filter (10) for removing dust and other contaminants can be incorporated in the flow path and the filter can also incorporate a fine filtering stage to produce a secondary clear air flow which can be directed into the detector to prevent smoke particles from settling on critical components of the detector.

Abstract: A smoke detector (2) which operates on the scattered light principle comprises a detector chamber (4) through which a light beam (10) passes. A series of collimator discs (24, 26, 28) with apertures of progressively increasing size are associated with the light source (6) to prevent glints of light from entering the zone of the chamber at which detection occurs as a result of the presence of scattered light induced by the presence of smoke particles. A light absorber (12) at the end of the detector chamber remote from the light source uses a target surface in the form of an asymmetric cone (42) onto which the beam is directed. The design of the collimator discs and light absorber reduce the occurrence of stray light, leading to increased sensitivity.

Abstract: A method and system for monitoring integrity of a filter (25) of a smoke or fire detector system. The system has a detector chamber (14) into which light is passed from a light source incorporated into a light source control circuit (10). Scattered light is detected by a light scatter detector (12). Controller circuit (16) receives signal from the detector (12) and makes a cumulative count over time of the number of dust particles detected.